i also had slight cracking in the highs with my D2000s, tho i'm not sure if it's caused by the headphones not being burn-in enough or the amp.. anyway it doesn't happen anymore ( after i ran the amp and the D2000s on high volume probably at around 3oclock position for 3 days or so), the thing is i never experienced it with my meier aria so i would guess it's the amp
Edit: up is high gain, tho i didn't need high gain on my D2000 just turned the volume up. btw you might like 2 consider rolling the amp, my D2000 sounds great with the 2228/8565 combo and gives more power(which would probably reduce the battery life, nothing dramatic i have noticed). the best way to go is to contact Hiflight and get some advice on opamps they're really easy to change. from the opamps that came with the D10 i found that 8532/8656 sounds better then stock with D2000, gives more power i think, you might like 2 try it, tho it doesn't give as transparent sound